1. Field of the Invention
The present invention relates to a washer pump for automobiles for supplying a cleaning fluid selectively to two supply channels for washing a windshield and a rear window, for example, of an automobile.
2. Description of the Prior Art
There are known various cleaning-fluid supply systems used for washing the windshield and the rear window of a motor vehicle, and most of the known cleaning-fluid supply systems comprise two washer pumps provided one for the washing of the windshield and the other for the washing of the rear window. The known systems having two pumps are costly to manufacture and occupy a relatively large space for installation thereof. With the foregoing difficulties in view, there have been proposed improved cleaning-fluid supply systems capable of washing the windshield and the rear window selectively by utilizing a single washing pump. One of such improved systems includes a differential pressure-operated valve associated with a washer pump for switching the flow of a cleaning fluid discharged from the washer pump, as disclosed in Japanese Patent Laid-open Publication No. 60-6096. Another improved system proposed by the present inventors includes a float valve associated with a washer pump for switching the direction of flow of the cleaning fluid, as disclosed in Japanese Patent Laid-open Publication No. 62-244741. This system is simple in construction and can be manufactured less costly.
The known automobile washer pumps of the centrifugal type generally have a maximum pump efficiency of about 25% or less. This is because the centrifural washer pumps have a circular pump chamber in which an impeller is rotatably disposed with a annular clearance defined between the circular pump chamber and the impeller. The clearance is determined by the amount of the cleaning fluid to be pressurized in the pump chamber. The pressurized cleaning fluid is discharged from the pump chamber through an outlet which extends tangentially to the circular pump chamber. During that time, however, the pressurized cleaning fluid flows back to the pump chamber due to the circular shape of the pump chamber, thus lowering the efficiency of the washer pump.
Various attempts proposed reduce the clearance between the pump chamber and the impeller are known, such as disclosed in Japanese Utility Model Publication No. 55-48156, for example. The disclosed pump is a so-called single-suction pump or a so-called double-suction pump irrespective of the size of the pump and has an impeller rotatable in only one direction. The impeller is disposed in a volute casing designed so that its cross-sectional area increases constantly toward the outlet. The disclosed pump of this construction is not suited for an automobile washer pump whose impeller is rotated in either direction to force the cleaning fluid selectively to two supply channels.
Differing from the general centrifural pump described above, the washer pump for automobiles has a pump chamber which is not the same as the volute chamber or casing as disclosed in the Japanese Utility Model Publication No. 55-48156 but is of a circular shape, such as shown in Japanese Patent Laid-open Publication No. 60-6096 stated above. In the circular pump chamber, there is disposed an impeller having circumferentially spaced radial vanes with an annular space or clearance defined between the peripheral wall of the pump chamber and the periphery of the impeller. The impeller is driven to rotate in either direction so that the pump chamber has two outlets leading to two washer nozzles. The washer pump of the foregoing construction has a substantially uniform pressure characteristic in either direction, however, due to a relative low pressure difference created between the two outlets, it occurs likely that a sealing valve is not shifted in position even when the direction of rotation of the impeller is changed. Consequently, a reliable delivery of the cleaning fluid to the selected washer nozzle is difficult to obtain.